Plants make bees remember them fondly with a jolt of caffeine

Foraging bees get a morning buzz through plant nectar that enhances memory.

As tiny as they are, bees are an incredible source of information for scientists, contributing to our knowledge in areas from agriculture to navigation. Just last week, we reported that bees use the electric fields of flowers to identify profitable plants, an ability that helps them forage more efficiently. A study in today’s issue of Science identifies another surprising cue that can play a significant role in bees' foraging behavior: caffeine.

Several plants, including species in the genuses Coffea and Citrus, produce nectar that contains caffeine; the concentration of caffeine in some of these flowers rivals that in a cup of instant coffee. We know what effects caffeine has on humans, but how does caffeinated nectar affect bees pollinating these plants?

To answer this question, the researchers taught bees to associate the odor of a particular chemical, called 1-hexanol, with a sugary reward. For some of the bees, the scientists added a small dose of caffeine to the sucrose reward solution in order to determine whether the consumption of caffeine affected how well the bees learned or remembered the association.

There was a small effect of caffeine on the rate of learning: bees that were given caffeine-laced nectar learned to associate the scent with the reward a bit faster than the bees that weren't given caffeine. Where the researchers saw the biggest difference, however, was in the bees’ long-term memory. When given caffeine, bees were three times more likely to recall the association 24 hours after being trained, and twice as likely to remember it 72 hours later.

The researchers were able to rule out the possibility that the caffeine made the bees more responsive to scent. Instead, the caffeine appeared to affect the bees’ cognition in some way.

Probing a bit deeper, the researchers then turned to the question of how, exactly, caffeine enhanced the insects’ memories. Although bee and human brains are quite different in terms of structure, they function in many similar ways. A group of neurons in the bee brain called “Kenyon cells” are somewhat homologous to our hippocampal neurons, which play a role in associative learning. The researchers recorded activity from bees' Kenyon cells, and found that caffeine increases these neurons’ excitability, making them more likely to fire in response to sensory stimuli. The more responsive these neurons are, the faster the bees’ brains can make the connection between the scent stimuli and the sweet reward.

But there’s a limit to the advantageous effects of caffeine; too large a dose can be toxic to insects. As a precaution, bees have developed the ability to detect the drug—and avoid it—in high concentrations. So caffeinated plants must toe the line, dosing their nectar with enough caffeine to help bees remember them, but not enough to drive the bees off. Plants that can successfully manipulate the bees’ behavior are rewarded with faithful pollinators that are “buzzed” on just enough caffeine to keep them coming back.

If it weren't for the bees that picture would look delicious! Heck it still kinda does, I want a mocha now. You tried to teach me about some science and all I want is caffeine and chocolate, and maybe honey. Great, good job!

I do wonder how this information might be used. Selective breeding to make plants more or less appealing to Bees perhaps?

Florists might benefit from selling Bee unfriendly blooms to Bee fearing consumers. Crops yields might be increased by growing a crop with just the right caffiene kick. Of course such manipulations are probably ill advised for biodiversity.

Bees are not the only pollinators, but I would be unsurprised if they discovered caffiene had similar effect on other related families.

Caffeine production has been found in plenty of plants and has been well known to affect insects for some time.

In most instances, it is actually a poison to keep insects away, some even have caffeine and related radicals coating their stems and leaves. Insects which crawl and are more likely to consume the plant or buds are especially susceptible. The caffeine stimulates the insect to the point that it either can't function or is more easily caught (noticed) by predators, not to mention the dehydration.

Caffeine production has been found in plenty of plants and has been well known to affect insects for some time.

In most instances, it is actually a poison to keep insects away, some even have caffeine and related radicals coating their stems and leaves. Insects which crawl and are more likely to consume the plant or buds are especially susceptible. The caffeine stimulates the insect to the point that it either can't function or is more easily caught (noticed) by predators, not to mention the dehydration.

Are you sure? I think the plants suddenly stops giving the insect caffeine. The insect then questions all meaning in its sad, drab, caffeine-less world and goes on a rampage until it finds a plant that does supply the caffeine, or dies.

Thanks for the story. Learning about interaction between plants and animals is always of great interest. I used to live in a small village and I had the opportunity to watch bees at work as they enjoyed my hibiscus. They are fascinating animals, it is quite easy to observe them closely. If you don't move or make brusque gestures, they will not feel threatened and will not attack you. Even for a non-scientist, it is clear that they act in an organized and intelligent way.

Kate Shaw Yoshida / Kate is a science writer for Ars Technica. She recently earned a dual Ph.D. in Zoology and Ecology, Evolutionary Biology and Behavior from Michigan State University, studying the social behavior of wild spotted hyenas.